A matrix converter can connect each phase of an AC power supply to output phase through a circuit structure of a bidirectional switch having a self-extinction capability and can directly convert an AC power into any voltage and frequency. In order to forcibly switch a current flowing to the switch, however, it is necessary to provide a unique switching sequence. The switching sequence will be hereinafter referred to as a commutating sequence. A switching sequence of a PWM cycloconverter has been disclosed in Patent Document 1 and Patent Document 2.
Examples of a method of creating a commutating sequence include a method of creating a commutating sequence based on an interswitch voltage polarity signal obtained by using a circuit for deciding a polarity of voltage of a switching device and a method of creating a commutating sequence based on an output current direction signal obtained by an output current direction detection circuit for deciding a direction of an output current flowing from a switching device (for example, Patent Document 3 and Patent Document 4). The communicating sequence which based on a PWM signal which is output is often created in a logic circuit and it is necessary to take a certain time in consideration of a switching time of the switching device. For this reason, an error is made between a voltage command value and an output voltage which is actually output. The error is generated depending on a state of a voltage of a power supply, and a voltage polarity and a voltage in the switching device which act as an information source of the communicating sequence. When a current flows to the bidirectional switch, furthermore, a voltage drop is caused in respect of a characteristic of a semiconductor device so that an error of the output voltage is made. Patent Document 5 compensating the problem by previously correcting the error into a command and Patent Document 6 eliminates the problem by using such a communicating sequence as not to make an error. In the matrix converter, generally, a PWM pulse having one-phase switching stopped is set to reduce a switching loss (Non-Patent Document 1, FIG. 2 and Non-Patent Document 2, FIG. 8). Moreover, Non-Patent Document 3 has proposed a matrix converter using a direct torque control.    Patent Document 1: JP-A-11-341807    Patent Document 2: JP-A-2000-139076    Patent Document 3: JP-A-2000-2724    Patent Document 4: JP-A-2001-165966    Patent Document 5: JP-A-2003-309975 (FIGS. 6 and 7)    Patent Document 6: EP1306964 (FIG. 5)    Non-Patent Document 1: “Trend of Direct AC/AC Converters and Related Technologies—Matrix Converter (PWM Controlled Cycloconverters)”, Japan Industry Application Society Conference 1-S3-2 (2004)    Non-Patent Document 2: “Trend of Direct AC/AC Converters and Related Technologies—Direct AC-AC Converters with DC Link”, Japan Industry Application Society Conference 1-S3-3 (2004)    Non-Patent Document 3: Domenico Casadei et al.: “The Use of Matrix Converters in Direct Torque Control of Induction Machines”, IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 48, NO. 6, DECEMBER 2001